This invention relates to the extraction of volatile oils from plant material and is particularly (though not exclusively) concerned with the extraction of volatile oils from turmeric (Curcuma spp.).
The extraction of volatile oils from turmeric and other plant materials is usually undertaken using steam distillation. It is conventional, for most plant materials, to steam distil the plant material after it has been dried, which may involve natural drying in the sun or may be some form of oven drying.
Fresh material is not traditionally steam distilled for a number of reasons. These include the fact that capacity limitations may mean that a crop of fresh material cannot be distilled before it has spoiled or rotted. Other reasons why the fresh material is not steam distilled include the difficulties experienced in steam distillation of a wet vegetable mass, e.g. tracking of the steam through the bed of plane material and the tendency of the vegetable material to form an amorphous mass of plant material.
In the case of Curcuma, it has hitherto been assumed that it is not possible to extract the curcuminoids from the dry plant residue after the material has been distilled wet.
The process used hitherto for extracting volatile oils has thus been based on the traditional first step of drying the harvested plant material; and the stages of the overall process, starting with turmeric and including the additional step of extracting curcuminoids, are thus:
(1) dry the harvested plant material;
(2) steam distil the dried plant material;
(3) separate the condensed oils from the aqueous layer;
(4) dry the residue from step (2);
(5) subject the dried residue from step (4) to solvent extraction; and
(6) remove solvent to produce the required curcuminoids.
The solvents employed in step (5) above were generally ethanol or acetone or a combination of alcohol and ketone solvents to extract the curcuminoids.
A further limitation of steam distillation of a large mass of plant material is that the process is very energy-inefficient. If one calculates the energy required to distil off the volatile oils and compares this to the energy used to achieve this end, then it is apparent that the process, in most steam distillation units, is very inefficient, with only a few percent of the input energy being required to volatilise the oils, the rest going to waste. The energy waste is compounded by the fact that cooling is required to condense the oils after distillation and the steam stream is also condensed in the process. The general inefficiency of the process is further manifest by the long cycle times to achieve a reasonable yield. For Curcuma this may typically be between 16 hours and 20 hours.
Furthermore, we have observed that the effect of the initial drying process is to reduce significantly the yield of the oils and other components that are sought from the production process.